Welding may be used to join two or more metal substrates. In general, welding may include clamping a workpiece, e.g., the two or more metal substrates to be joined, between two electrodes with a force, and passing an electrical current from one electrode, through the workpiece, to the second electrode for a duration to thereby complete an electrical circuit. The electrical current causes sufficient heat due to electrical resistance to build up at an interface between the metal substrates, i.e., at a faying surface of each metal substrate, so as to partially and momentarily melt the interface. Therefore, a combination of the force, current, and weld duration forms a weld nugget, i.e., the weld, to join the metal substrates.
Although the weld is formed within an interior of the workpiece between faying surfaces of the metal substrates, the weld may be perceivable as an indentation on an exterior surface of the workpiece. That is, each electrode may form an indentation having a depth at a point of contact with the metal substrate.